Info from Synapse Site:
In 1999 we invented and launched the Missing Link with the goal of helping to make aftermarket turbo systems more reliable. It has today become an industry standard from which beginners learn that turbos can be reliable and with confidence move on to their next stage of power.
The Missing Link works by mounting between the intake manifold signal and the factory map sensor. It completely blocks boost pressure from the MAP sensor to keep it from being destroyed by boost pressure, while maintaining the vacuum signal necessary to keep the factory computer from seeing the additional boost pressure.